Field of the Invention
The present invention relates to a charging/discharging control circuit that controls charging and discharging of a secondary cell, a charging/discharging control device, and a battery device, and particularly, to a technology of preventing a current from excessively flowing to a mechanism connected to a battery or a battery device.
Background Art
FIG. 4 illustrates a circuit diagram of a conventional battery device.
The conventional battery device is configured to include a secondary cell 11, an Nch discharging control field effect transistor 12, an Nch charging control field effect transistor 13, a charging/discharging control circuit 14, resistors 22 and 31, a capacity 32, and external terminals 20 and 21. The charging/discharging control circuit 14 is configured to include a control circuit 15, an over-current detection circuit 16, an over-current detection terminal 19, a charging control signal output terminal 41, a discharging control signal output terminal 42, a positive electrode power source terminal 44, and a negative electrode power source terminal 43. The over-current detection circuit 16 is configured to include a comparator circuit 18 and a reference voltage circuit 17.
Next, an operation of the conventional battery device will be described.
When a load is connected between the external terminals 20 and 21 and a current flows, a potential difference is generated between a negative electrode of the secondary cell 11 and the external terminal 21. The potential difference is determined by a current amount I1 of the current flowing between the external terminals 20 and 21, a resistance value R12 of the Nch discharging control field effect transistor 12, and a resistance value R13 of the Nch charging control field effect transistor 13, and is expressed as I1×(R12+R13). The voltage of the over-current detection terminal 19 is equal to the voltage of the external terminal 21. The comparator circuit 18 compares the voltage of the reference voltage circuit 17 with the voltage of the over-current detection terminal 19, and when the voltage of the over-current detection terminal 19 is higher, the Nch discharging control field effect transistor 12 is turned off to provide over-current protection.
A set over-current detection current value is IDOP, the voltage of the reference voltage circuit 17 is V17, the resistance value of the Nch discharging control field effect transistor 12 is R12, and the resistance value of the Nch charging control field effect transistor 13 is R13. The voltage of the external terminal 21 when a threshold voltage is reached at which the comparator circuit 18 outputs a detection signal is V17. At this time, the current flowing between the external terminals 20 and 21 is calculated by dividing the voltage of the external terminal 21 by the sum of the resistance values of the Nch discharging control field effect transistor 12 and the Nch charging control field effect transistor 13, and is expressed as IDOP=V17/(R12+R13).
The voltage of the over-current detection terminal of the charging/discharging control circuit when the comparator circuit 18 outputs a detection signal is referred to as an over-current detection voltage.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-104956